1. Field of the Invention
The present invention relates to a lithography apparatus and a lithography method and, in particular, to a lithography apparatus and a lithography method for forming patterns by using electron beams in a vacuum state.
2. Related Art
A photolithography technique which takes a part of the development of miniaturization of semiconductor devices is only a process, in which a pattern is generated, in semiconductor manufacturing processes and is very important. In recent years, with the advancement in integration density of an LSI, circuit line widths required for semiconductor devices are miniaturized year by year. In order to form desired circuit patterns on the semiconductor devices, precise original patterns (to be also referred to as a reticle or a mask) are required. In this case, an electron beam writing technique has an essentially excellent resolution, and is used in production of precise original patterns.
FIG. 10 is a conceptual diagram for explaining an operation of a variable-shaped electron beam lithography apparatus. The variable-shaped electron beam lithography apparatus operates as follows. An oblong, for example, rectangular opening 411 to shape an electron beam 330 is formed in a first aperture plate 410. A variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired oblong shape is formed in a second aperture plate 420. The electron beam 330 irradiated from the charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector, passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and is irradiated on a target object 340 placed on a stage continuously moving in one predetermined direction (for example, an X direction). More specifically, an oblong shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a write region of the target object 340 placed on the stage continuously moving in the X direction. A scheme which causes an electron beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is a variable-shaping scheme.
FIG. 11 is a conceptual diagram showing a housing configuration of the lithography apparatus. In FIG. 11, in the electron beam lithography apparatus, a stage 305 on which a target object 301 is placed is accommodated in a write chamber 303. On the write chamber 303, an electro-optic lens barrel 302 on which the electro-optic system described above is mounted is arranged. In a writing operation, the electro-optic lens barrel 302 and the write chamber 303 are vacuumed by a vacuum pump 310, and a pattern is formed on the target object 301 in vacuum. In this case, in order to install, remove, or check the stage 305 in the write chamber 303, an opening 320 having a size which is enough to carry the stage 305 in or out. While the electro-optic lens barrel 302 and the write chamber 303 are vacuumed, the opening 320 is closed by a door 331. The door 331 can be opened and closed, and is fixed to a side surface with a screw or the like.
In this case, when the inside and outside of the write chamber 303 are in an atmospheric pressure, any problem is not posed. However, since a pressure difference occurs in the inside and outside of the write chamber 303 when the write chamber 303 is set in a vacuum state, a circumferential surface of the write chamber 303 is deformed. At this time, since the rigidity of a side surface in which the opening 320 is formed and the rigidity of a side surface in which the opening 320 is not formed are different from each other, amounts of deformation are different from each other to tilt the electro-optic lens barrel 302 to a side of the low-rigidity side surface in which the opening 320 is formed. When the electro-optic lens barrel 302 is tilted, the trace of an electron beam is misaligned to disadvantageously cause an error in size of a pattern to be formed. In particular, an amount of deformation of the write chamber 303 changes depending on a variation in atmosphere. For this reason, an angle θ at which the electro-optic lens barrel 302 is tilted changes depending on a variation in atmosphere, and an error of a write position changes accordingly. In particular, a higher pattern-forming accuracy is required with miniaturization of a circuit line width in recent years, and thus deterioration in pattern-forming accuracy caused by positional misalignment by a variation in atmosphere is not negligible. In a conventionally, this problem is addressed by correcting a deflection position of an electron beam. However, this correction cannot be easily performed when an amount of deformation becomes large.
A technique (for example, see Japanese Unexamined Patent Publication No. 7-211612) which calculates an amount of field distortion caused by a variation in atmosphere by a projection optical system which exposes a mask image on a wafer to move a stage to an appropriate position is disclosed in a document.
As described above, the angle by which the electro-optic lens barrel is tilted on the weak side surface side on which the opening is formed changes depending on a variation in atmosphere, and an error in size of a pattern to be formed occurs disadvantageously. For this reason, a small tilt angle is desired, however, a measure for the small tilt angle has not been made.